Sharper images by focusing soft X-rays with photon sieves

Fresnel zone plates consisting of alternating transmissive and opaque circu lar rings can be used to focus X-rays(1). The spatial resolution that can b e achieved with these devices is of the order of the width of the outermost zone and is therefore limited by the smallest structure (20-40 nm) that ca n be fabricated by lithography today(2). Here we show that a large number o f pinholes distributed appropriately over the Fresnel zones make it possibl e to focus soft X-rays to spot sizes smaller than the diameter of the small est pinhole. In addition, higher orders of diffraction and secondary maxima can be suppressed by several orders of magnitude. In combination with the next generation of synchrotron light sources (free-electron lasers) these ' photon sieves' offer new opportunities for high-resolution X-ray microscopy and spectroscopy in physical and life sciences.